The present invention relates to method and apparatus for detecting cable length of a connecting cable between units in a video equipment or an information processing apparatus.
In the video equipment or information processing apparatus, frequency characteristic of a video signal or information signal transmitted is degraded corresponding to the length of a signal transmission cable connecting the units.
For example, in the connection of a television camera 13 and a camera control unit 14 shown in FIG. 2, as the lengths of connecting cables (e.g., coaxial cables) 15 and 16 between the television camera 13 and the camera control unit 14 is increased, the frequency characteristic of the video signal is increased degraded. As a result, it is necessary to compensate for this characteristic of the cable in the television camera 13 or the camera control unit 14. In order to compensate for the cable characteristic, a manual system in which the length of the cable is measured and the degree of compensation is selected corresponding to the length, and an automatic compensation system in which a cable length detection circuit for automatically detects the cable length and the compensation is made corresponding to the detected length have been proposed. A prior art of the automatic compensation system with the cable length detection circuit is shown in U.S. Pat. No. 4,151,490, for example. In this prior art, a reference signal is added to a video signal to be transmitted through a cable, at an input end of the cable, and a video signal is compensated in accordance with an amount of the attenuation of an amplitude of the reference signal at an output end.